Time-variant Reliability Analysis Of Harmonic Drive For Industrial Robots Under Multiple Failure Modes

As an important high-end manufacturing equipment,industrial robots are widely used in automobile assembly,electronic appliances and food processing industries.Domestic industrial robots generally have the problems of short Mean Time Between Failure(MTBF),frequent crashes,and poor precision retaining ability.Harmonic Drive,which is connected with servo motor to reduce speed and increase torque,is one of the key components of industrial robots.Because the Harmonic Drive directly bears the torque load under complex working conditions,its reliability directly affects the performance and safety of industrial robots.Therefore,it is of great significance to study the reliability of Harmonic Drive for industrial robots.At present,the reliability research of Harmonic Drive is mostly the time-invariant reliability analysis of single failure mode without considering the system reliability problem under multiple failure modes and the time-variant reliability problem.Therefore,it is necessary to study the time-variant reliability of Harmonic Drive for industrial robots under multiple failure modes,so as to scientifically evaluate its reliability and indicate the direction for optimization design.In view of the above problems,this thesis takes the short cup type Harmonic Drive commonly used in industrial robots as the research object,and mainly carries out the following research work:(1)The Failure Mode,Effects and Criticality Analysis(FMECA)method is used to analyze the failure modes of Harmonic Drive for industrial robots.To determine the weak parts of the system and major failure modes through Risk Priority Number(RPN).Based on the failure physics,the limit state functions of the major failure modes are established.(2)Based on the Vine Copula function,a method study of time-invariant reliability analysis under multiple failure modes is carried out.This method can transform the time-invariant reliability problem under multiple failure modes into a joint problem of the static reliability of single failure mode and the correlation analysis between failure modes.The random variable distribution types and parameters in each limit state function of Harmonic Drive for industrial robots are determined,and the correlation between failure modes is characterized by the Copula function.By comparing with the results of Monte Carlo Simulation(MCS),the effectiveness of the method and the necessity of considering the correlation between failure modes are verified.(3)Based on the above time-invariant reliability analysis method under multiple failure modes,a time-variant reliability analysis method under multiple failure modes is proposed.This method can transform the time-variant reliability problem under multiple failure modes into a joint problem of the time-variant reliability of single failure mode and the time-varying correlation analysis between failure modes.Considering the time-varying characteristics of the load and the degradation of the material performance in the actual use of Harmonic Drive for industrial robots,the time-varying limit state function of the major failure modes is established.Time-varying Copula function is used to describe the time-varying correlation between failure modes.By comparing with the results of MCS,the effectiveness of this method is verified.